Mechanical refrigeration systems, and related heat transfer devices such as heat pumps and air conditioners, using refrigerant liquids are well known in the art for industrial, commercial and domestic uses. Chlorofluorocarbons (CFCs) were developed in the 1930s as refrigerants for such systems. However, since the 1980s the effect of CFCs on the stratospheric ozone layer has become the focus of much attention. In 1987 a number of governments signed the Montreal Protocol to protect the global environment setting forth a timetable for phasing out the CFC products. CFC's were replaced with more environmentally acceptable materials that contain hydrogen or hydrochlorofluorocarbons (HCFC's). Subsequent amendments to the Montreal protocol accelerated the phase-out of these CFCs and also scheduled the phase-out of HCFCs. Thus, there is a requirement for a non-flammable, non-toxic alternative to replace these CFCs and HCFCs. In response to such demand industry has developed a number of hydrofluorocarbons (HFCs), which have a zero ozone depletion potential.
The importance of refrigeration systems, especially low temperature refrigeration systems, to the food manufacture, distribution and retail industries is fundamental. Such systems play a vital role in ensuring that food which reaches the consumer is both fresh and fit to eat. In such low temperature refrigeration systems the popular refrigerant employed has been chlorodifluoromethane (R-22 or HCFC-22), which has an ozone-depleting potential and will be phased out completely.
A number of patent publications have suggested replacements for HCFC-22. That is, these patent publications have suggested refrigerants or refrigerant compositions that can be used instead of HCFC-22 in new refrigeration systems to be built or installed. Among such patent publications there may be mentioned U.S. Pat. No. 5,185,094, U.S. Pat. No. 5,370,811, U.S. Pat. No. 5,438,849, U.S. Pat. No. 5,643,492, U.S. Pat. No. 5,709,092, U.S. Pat. No. 5,722,256, U.S. Pat. No. 6,018,952, U.S. Pat. No. 6,187,219 B1, U.S. Pat. No. 6,606,868 B1, U.S. Pat. No. 6,669,862 B1, published US application NO. US 2004/00691091 A1, and published European application nos. EP 0 430169 A1, EP 0 509 673 A1 and EP 0 811 670 A1. While all the mentioned US patents and published EP applications disclose ternary mixtures of difluoromethane (HFC-32), pentafluoroethane (HFC-125) and tetrafluoroethane (HFC134a) for use in refrigeration or air conditioning systems, they do not address the ability to replace HCFC-22 in existing R-22 refrigeration systems or systems suitable for use with R-22 refrigerant, particularly in low temperature refrigeration systems, while obtaining at least about 95% of the operating characteristics of R-22 without the necessity for modification of the system, especially without the necessity for adjustment or replacement of the expansion valve of the low temperature refrigeration system. Comparative examples provided later in the present specification of this application show that tertiary compositions within the scope of the prior art disclosure are not suitable for use in low temperature R-22 refrigeration systems. Those prior art compositions do not obtain at least about 95% of the operating characteristics of R-22 so as to enable one to use such compositions in low temperature R-22 refrigeration systems over a wide range of low refrigeration temperatures and ambient temperatures without the necessity for modification of the system.
In order to retrofit an existing low temperature refrigeration system employing HCFC-22 refrigerant with replacement refrigerant, it is necessary that that the replacement refrigerant operating characteristics, such as evaporator superheat, cooling capacity, refrigerant mass flow rate, efficiency, pressure and energy consumption, are substantially identical to that of the HCFC-22 refrigerant being replaced. This near match in properties of the replacement refrigerant to those of HCFC-22 are essential for their use in such existing low temperature refrigeration systems or systems designed for using R-22 refrigerant, without requiring equipment replacement or modification, e.g. replacement or modification of expansion valves of the low temperature refrigeration system. The solutions suggested by the industry for R-22 replacements, such as R-407A and R-407C refrigerants, do not solve this problem since they require modification of the systems in an attempt to match R-22 operating characteristics.